Forget that motorcycle crap, definitely go for a SA full face as you will be able to use it at all kinds of driving events including go-karting.
Check your local racing groups bulletin boards, people are getting rid of good quality equipment all the time. Just the other day I saw a nearly new helmet go for $75, the guy was retiring from racing and selling all his stuff.
For new try
SafeRacer.com and
SoloRacer.com, they often have stuff on clearance. Definitely go to a brick and motor store first so you can figure out your size and see what is comfortable.